OJ SPONGES 
brates, above the Infusoria, pass through what he teriiis 
the Gastrula stage of existence. That is, at one stage of 
their existence they possess a primitive digestive cavity 
or stomach (whence the name gastrula) and are then more 
or less alike. Thus he considers all such animals, beginning 
with sponges and extending to the lower vertebrates, as 
belonging to one group, of which the sponges form one di- 
vision which is closely allied to the corals. 
In 1889, appeared Lendenfeld’s Monograph of the 
Horny Sponges, in which he regards sponges as much 
higher than the Infusoria, in fact, they constitutea group 
of the coelenterata, (corals, jelly-fishes. etc.) This group, 
termed by him a Phylm, he proposes to call Mesodemalia. 
Dr Lendenfeld thinks sponges have highly defferentiated 
cells, aside from the collar cells, cells in which nervous act- 
ion originates, others in which muscular action takes 
place, separate cells for the formation and development of 
the spermatogoa and ova etc. Two great divisions only 
are made among sponges. Silicious, among which are in- 
cluded’ Horny Sponges, sponges without skeletons, and. 
